Electronic device with noise-cancelling force sensor
First Claim
1. A strain gauge, comprising:
- a layer of material configured to flex in response to pressure;
a first variable resistor mounted on the layer of the material;
a second variable resistor mounted on the layer of the material adjacent to the first variable resistor; and
a differential amplifier having first and second differential inputs that receive input from a bridge circuit and having an output at which a corresponding strain gauge output signal is provided, wherein the bridge circuit includes the first and second variable resistors, wherein the first variable resistor follows a path on the layer of material, wherein the second variable resistor follows the same path on the layer of material, and wherein the path is a serpentine path.
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Accused Products
Abstract
An electronic device may have a housing in which components such as a display are mounted. A strain gauge may be mounted on a layer of the display such as a cover layer or may be mounted on a portion of the housing or other support structure. The layer of material on which the strain gauge is mounted may be configured to flex in response to pressure applied by a finger of a user. The strain gauge may serve as a button for the electronic device or may form part of other input circuitry. A differential amplifier and analog-to-digital converter circuit may be used to gather and process strain gauge signals. The strain gauge may be formed form variable resistor structures that make up part of a bridge circuit that is coupled to the differential amplifier. The bridge circuit may be configured to reduce the impact of capacitively coupled noise.
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Citations
18 Claims
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1. A strain gauge, comprising:
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a layer of material configured to flex in response to pressure; a first variable resistor mounted on the layer of the material; a second variable resistor mounted on the layer of the material adjacent to the first variable resistor; and a differential amplifier having first and second differential inputs that receive input from a bridge circuit and having an output at which a corresponding strain gauge output signal is provided, wherein the bridge circuit includes the first and second variable resistors, wherein the first variable resistor follows a path on the layer of material, wherein the second variable resistor follows the same path on the layer of material, and wherein the path is a serpentine path. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A strain gauge, comprising:
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a layer of material configured to flex in response to pressure; at least one variable resistor mounted on the layer of the material; a differential amplifier having first and second differential inputs that receive input from a bridge circuit and having an output at which a corresponding strain gauge output signal is provided, wherein the bridge circuit includes the at least one variable resistor; and a coupling pad that balances how much noise is capacitively coupled to the first differential input with how much noise is capacitively coupled to the second differential input. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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16. A strain gauge, comprising:
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a layer of material configured to flex in response to pressure; a first variable resistor mounted on the layer of the material; a second variable resistor mounted on the layer of the material, wherein the second variable resistor overlaps the first variable resistor; and a differential amplifier having first and second differential inputs that receive input from a bridge circuit and having an output at which a corresponding strain gauge output signal is provided, wherein the bridge circuit includes the first and second variable resistors. - View Dependent Claims (17, 18)
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Specification